Paradigm shift of underwater echo sounding technology II—Experiment and actual sea trial

Abstract

The newly suggested “Paradigm-Shift-Echosounder” (PSE) for bathymetry survey was tested in a sea trial experiment using a prototype. Experiment was conducted at the depth of 30-80 m using 200 kHz signals transmitted 100 times per second and succeeded to obtain continuous bottom echo data. We also conducted a side scanning sonar experiment using 88 kHz signals, at a site with a depth more than 500 m and succeeded to obtain the echo of a 2 m x 5 m artificial reef moored at the depth of 50 m. Correlation processing was done and we managed to reconstruct a high-resolution echogram of the artificial reef. The prototype used in the trial experiments utilizes the 7th order Gold code sequence. Four cycles of carrier signals as 1 bit, the transmission signals are all phase-modulated. The pulse length of transmission signal is 2.54 ms for 200 kHz. As there are 127 Gold codes, transmission signals of the same code are repeated every 1.28 seconds. The receiving signals are then processed by the correlator, with a shift register length of 4064 stages by 8-times sampling frequency for carrier frequency. There are 127 kinds of replicas of correlator, and the numbers of “Exclusive OR + Summation” circuits are also 127.